‘The Wolf in Sheep’s Clothing’ is a well-known phrase and a well-known fable. Most people would attribute the fable to Aesop, the master fabulist of classical times. However, was we will discuss later on in our analysis of this story, this is inaccurate.
Before we analyse the meaning and history of the ‘Wolf in Sheep’s Clothing’ fable, and the origins of the phrase, it might be worth summarising its ‘plot’.
‘The Wolf in Sheep’s Clothing’: summary
A wolf wanted to catch some sheep to eat, but he was unable to do so because the shepherds were watching their flocks too closely.
But one night, the wolf found a sheep skin that had been sheared from a sheep and then cast aside and forgotten about. When the next day came, the wolf dressed himself in the sheepskin, and went into the pasture where the sheep were grazing. A little lamb, little suspecting that this new sheep was actually a wolf in disguise, began following the wolf about, and the wolf took his chance and caught and ate the poor lamb.
That evening, the wolf entered the fold with the flock. But it just so happened that the shepherd fancied making some mutton broth that evening. He went to the fold and caught the first sheep he found, which was actually the wolf disguised in sheepskin. And thus the wolf was mistaken for a sheep and was caught and killed by the shepherd.
‘The Wolf in Sheep’s Clothing’: analysis
The moral of ‘The Wolf in Sheep’s Clothing’ is often summarised as follows: The evil doer often comes to harm through his own deceit.
This is true: unlike some other famous animal fables – notably, the fable of the ‘hare and the tortoise’ where the moral usually ascribed to the fable tells only 
half the story – the moral message of ‘The Wolf in Sheep’s Clothing’ is straightforward and unequivocal. If the wolf had not disguised himself as a sheep, the shepherd would never have mistaken him for one and he wouldn’t have been slaughtered to provide the meat for the shepherd’s mutton broth.
So the meaning of the fable is fairly clear. However, most people attribute the fable to Aesop, even though there is no evidence that the fable was one of his. Many editions of Aesop’s Fables omit the fable of the wolf in sheep’s clothing for this reason: although it has the ‘ring’ of Aesop’s other fables, it doesn’t appear to have been his work.
What’s more, the phrase or idiom ‘wolf in sheep’s clothing’ comes not from the fable, but from the Bible: it originated in a one of Jesus’ sermons. Jesus tells his disciplines: ‘Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves’ (Matthew 7:15). Thus two well-known phrases – ‘beware of false prophets’ and ‘wolf in sheep’s clothing’ – appear to have their origins not only in the same sermon by Jesus but the same sentence from that sermon.
Around the same time, a Latin proverb is recorded which reads: Pelle sub agnina latitat mens saepe lupina (‘Under a sheep’s skin often hides a wolfish mind’); whether or not this was derived from the sermon quoted above, or evolved independently of it, we cannot say for sure. But what we can say with some certainty is that there’s no evidence of a fable containing a wolf in sheep’s clothing before medieval times, i.e., over a millennium after the New Testament was written. Its author was a 12th-century Greek rhetorician named Nikephoros Basilakis, whose book of rhetorical exercises, Progymnasmata, contains a version of the fable, prefaced by the moral message: ‘You can get into trouble by wearing a disguise’.
So the fable added the other moral message to the story. Jesus’ use of the idiom is merely a warning to the ‘sheep’ in the scenario (his ‘flock’, if you will) that sometimes the devious and evil adopt the appearance of innocence and goodness in order to dupe us. But the moral for which the fable is now best-known relates to the end of the story, with the wolf being, as it were, ‘hoist with its own petard’ (to use another famous idiom, this time derived from Hamlet).
What’s more, Aesop wasn’t the first person to write animal fables. Several centuries earlier, Hesiod had written one about a hawk and a nightingale, while a poet named Archilochus penned several, including one about an eagle and a vixen, and one about a fox and a monkey. But Aesop would turn the fable into a popular form. William Caxton printed the first English translation of the Fables in 1484, enabling such phrases as ‘sour grapes’ and ‘to cry wolf’ to enter the language. But not, as we have seen, ‘wolf in sheep’s clothing’.